The Cook Islands and Niue became New Zealand's first Pacific colonies in 1901 and then protectorates. From 1965 the Cooks were self-governing; so was Niue from 1974. Tokelau came under New Zealand control in 1925 and remains a non-self-governing territory.[3]

The Ross Dependency comprises that sector of the Antarctic continent between 160° east and 150 west longitude, together with the islands lying between those degrees of longitude and south of latitude 60.[4] The British (Imperial) government took possession of this territory in 1923 and entrusted it to the administration of New Zealand. Neither Russia nor the United States recognises this claim, and the matter is left unresolved (along with all other Antarctic claims) by the Antarctic Treaty, which serves to mostly smooth over these differences. It is largely uninhabited, apart from scientific bases.

New Zealand citizenship law treats all parts of the realm equally, so most people born in New Zealand, the Cook Islands, Niue, Tokelau and the Ross Dependency before 2006 are New Zealand citizens. Further conditions apply for those born from 2006 onwards.[5]

A governor-general represents the head of state (Elizabeth II, in her capacity as Queen of New Zealand) in the area of the realm. Essentially, Governors-General take on all the dignities and reserve powers of the head of state. From 31 August 2011 until 31 August 2016 the Governor-General was Rt Hon Sir Jerry Mateparae. Dame Patsy Reddy was appointed to assume the position on 14 September 2016.[6][7]

Both the Cook Islands and Niue are self-governing states in free association with New Zealand. The details of their free association arrangement are contained in several documents, such as their respective constitutions, the 1983 Exchange of Letters between the governments of New Zealand and the Cook Islands, and the 2001 Joint Centenary Declaration. As such, the Parliament of New Zealand is not empowered to unilaterally pass legislation in respect of these states. In foreign affairs and defence issues New Zealand acts on behalf of these countries, but only with their advice and consent.

As the Governor-General is resident in New Zealand, the Cook Islands Constitution provides for the distinct position of Queen's Representative. This individual is not subordinate to the Governor-General and acts as the local representative of the Queen in right of New Zealand. Since 2013, Tom Marsters is the Queen's Representative to the Cook Islands. (Marsters was preceded by Sir Frederick Tutu Goodwin.) This arrangement effectively allows for the de facto independent actions of internal and most external areas of governance.

In the Cook Islands and Niue the New Zealand High Commissioner is the diplomatic representative from New Zealand. John Carter (since 2011) is the New Zealand High Commissioner to the Cook Islands. Mark Blumsky was the New Zealand High Commissioner to Niue from 2010 until he was replaced by Ross Ardern in early 2014.

Despite their close relationship to New Zealand, both the Cook Islands and Niue maintain some diplomatic relations in their own name. Both countries maintain High Commissions in New Zealand and have New Zealand High Commissioners resident in their capitals. In Commonwealth practice, High Commissioners represent their governments, not the Head of State.

the Ross Dependency, which forms part of Antarctica. It is constitutionally part of New Zealand.[8] However, application of Sovereignty within the Dependency is subsequent upon the enforcement of terms found within the Antarctic Treaty

Tokelau has a lesser degree of independence than the Cook Islands and Niue, and had been moving toward free association status. New Zealand's representative in Tokelau is the Administrator of Tokelau and has the power to overturn rules passed by the Parliament of Tokelau. In referenda conducted in 2006 and 2007 by New Zealand at the United Nations' request, the people of Tokelau failed to reach the two-thirds majority necessary to attain a system of governance with equal powers to that of Niue and the Cook Islands.[9]

Within New Zealand there exists some support[10][11] for a New Zealand republic. Should New Zealand become a republic it will retain the Ross Dependency and Tokelau as dependent territories and the Realm of New Zealand would continue to exist without New Zealand, the Ross Dependency and Tokelau.[12] This would not be a legal hurdle to a New Zealand republic as such, and both the Cook Islands and Niue would retain their status as associated states with New Zealand, as New Zealand shares its Head of State with the Cook Islands and Niue. However, a New Zealand republic would present the issue of independence to the Cook Islands and Niue. Thus, a number of options for the future of the Realm of New Zealand exist should New Zealand become a republic:

A New Zealand republic with the Cook Islands and Niue remaining in free association with New Zealand, but retaining the Queen as their head of state;

A New Zealand republic with the Cook Islands and Niue having a new republican head of state as their head of state and becoming independent states;

A New Zealand republic with the Cook Islands and Niue having their own heads of state, but retaining their status of free association with New Zealand.[12]